1. Field of the Invention
The present invention relates to an image processing apparatus which is used in a facsimile communication, an image data base, or the like.
2. Related Background Art
In recent years, as a method of encoding a natural image (multivalue color image), there has been proposed a method whereby an image is divided into blocks each comprising a plurality of pixels, a DCT (discrete cosine transform) is executed for each block, a coefficient of the DCT is quantized, and a Huffman code is assigned.
However, in the above conventional method, since a high frequency portion of the DCT coefficient is roughly quantized in order to raise the encoding efficiency, a ringing occurs in an edge portion of a reproduction image, particularly, in a portion of a character and a blur of the peripheral portion of the character remarkably deteriorates the quality of image.
Such a problem is not limited to the encoding method as mentioned above but also similarly occurs in other encoding methods such as orthogonal transformation encoding, vector quantization, and the like.
On the other hand, techniques for extracting an edge component and executing an encoding according to the extracted edge component have been proposed by the same assignee of the present application in U.S. Pat. Nos. 4,797,945 and 4,887,151 and U.S. patent application Ser. Nos. 185,024, 261,276, 312,755, and 362,014, now U.S. Pat. No. 5,089,884.
In addition, a technique for executing a process according to an edge component when encoded image data is decoded has been proposed by the same assignee of the present application in U.S. patent application Ser. No. 146,084, now U.S. Pat. No. 5,023,919.
However, the further improvement is demanded to solve the above problems and to improve both of the encoding efficiency and the reproducibility of the image.